Highly Resilient Protocol Servicing in Network-Attached Storage

ABSTRACT

A mechanism is provided in a data processing system for protocol servicing in network-attached storage. A protocol service executing in the data processing system in a clustered file system establishes a high priority recovery thread. The high priority recovery thread monitors health counters that count total requests in and total requests out for a client accessing a network-attached storage device via the protocol service. The high priority recovery thread determines a category of health of the protocol service based on the health counters. The mechanism takes corrective action based on the category of health of the protocol service.

BACKGROUND

The present application relates generally to an improved data processingapparatus and method and more specifically to mechanisms for highlyresilient protocol servicing in network-attached storage.

A clustered file system is a file system that is shared by beingsimultaneously mounted on multiple servers. Clustered file systems canprovide features like location-independent addressing and redundancywhich improve reliability or reduce the complexity of the other parts ofthe cluster. Parallel file systems are a type of clustered file systemthat spread data across multiple storage nodes, usually for redundancyor performance.

Network-attached storage (NAS) provides both storage and a file system,like a shared disk file system on top of a storage area network (SAN).NAS is file-level computer data storage connected to a computer networkproviding data access to a heterogeneous group of clients. NAS not onlyoperates as a file server, but is specialized for this task either byits hardware, software, or configuration of those elements. NAS is oftenmanufactured as a computer appliance, a specialized computer built fromthe ground up for storing and serving files, rather than simply ageneral purpose computer being used for the role.

NAS systems are networked appliances which contain one or more harddrives, often arranged into logical, redundant storage containers orredundant array of independent disks (RAID). Network-attached storageremoves the responsibility of file serving from other servers on thenetwork. They typically provide access to files using network filesharing protocols such as network file system (NFS) or server messageblock/common Internet file system (SMB/CIFS).

SUMMARY

In one illustrative embodiment, a method, in a data processing system,is provided for protocol servicing in network-attached storage. Themethod comprises establishing, by a protocol service executing in thedata processing system in a clustered file system, a high priorityrecovery thread. The method further comprises monitoring, by the highpriority recovery thread, health counters that count total requests inand total requests out for a client or clients accessing anetwork-attached storage device via the protocol service. In addition,the health counters may monitor specific types of protocol operationssuch as file opens, file locks, etc. The method further comprisesdetermining, by the high priority recovery thread, a category of healthof the protocol service based on the health counters. The method furthercomprises taking corrective action based on the category of health ofthe protocol service.

In other illustrative embodiments, a computer program product comprisinga computer useable or readable medium having a computer readable programis provided. The computer readable program, when executed on a computingdevice, causes the computing device to perform various ones of, andcombinations of, the operations outlined above with regard to the methodillustrative embodiment.

In yet another illustrative embodiment, a system/apparatus is provided.The system/apparatus may comprise one or more processors and a memorycoupled. to the one or more processors. The memory may compriseinstructions which, when executed by the one or more processors, causethe one or more processors to perform various ones of, and combinationsof, the operations outlined above with regard to the method illustrativeembodiment.

These and other features and advantages of the present invention will bedescribed in, or will become apparent to those of ordinary skill in theart in view of, the following detailed description of the exampleembodiments of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention, as well as a preferred mode of use and further objectivesand advantages thereof, will best be understood by reference to thefollowing detailed description of illustrative embodiments when read inconjunction with the accompanying drawings, wherein:

FIG. 1 depicts a pictorial representation of an example clustered filesystem in which aspects of the illustrative embodiments may beimplemented;

FIG. 2 is a block diagram of an example data processing system in whichaspects of the illustrative embodiments may be implemented;

FIG. 3 is a Hock diagram illustrating a protocol service in accordancewith an illustrative embodiment; and

FIG. 4 is a flowchart illustrating operation of a protocol service inaccordance with an illustrative embodiment.

DETAILED DESCRIPTION

The illustrative embodiments provide a mechanism for highly resilientprotocol servicing in network-attached storage (NAS). In a currentapproach, NAS devices monitor the health of their protocol services,usually NFS and/or CIFS, and take corrective action when they detectservice degradation. The NAS generally performs monitoring byconstructing a minimal protocol operation and sending that operation tothe device. In NFS, the minimal protocol operation may be a NULLoperation, for example. If the NAS does not receive a response within acertain period of time within a certain number of tries, the NAS deemsthe service unresponsive and takes corrective action. The correctiveaction typically involves completely restarting the service.

There are several problems with the current approach that mainly surfaceunder heavy protocol load conditions. Under these circumstances, networkprocessing of a particular request (i.e., the NULL health operation) maybe delayed even though overall protocol processing is proceeding at aheavy rate. Note also that the monitor adds to the protocol load, whichexacerbates the situation. That is, monitoring itself can contribute tothe node being deemed unhealthy.

Also note that no matter how one adjusts the time interval that themonitor waits, there will always be a load level at which the latency ofthe response exceeds the time interval. One cannot adjust the approachto completely eliminate the case where the monitor incorrectly concludesthat the service is unresponsive.

In addition, restarting the service in these conditions causes furtherproblems. When the service is restarted, all clients are disrupted andrespond by retransmitting their outstanding requests. This increases thetotal protocol load and often swamps the newly restarted service leadingto a cycle of restart/re-transmission/restart/re-transmission.

The mechanism of the illustrative embodiments moves the task of servicemonitoring from an outside source sending protocol operations to withinthe protocol service itself. Internally, the protocol keeps track ofwhether requests are being processed and, if so, at what rate, whetherrequests of a particular type or from a particular client are stalled,etc. Taking the monitoring data into account, the service can thencategorize its health and publicize its condition. In an exampleembodiment, the service may categorize its health as green, yellow, orred. Depending on this condition the service may be restarted,relocated, or left unmodified. These corrective actions can be taken byan external source or by the service itself.

The mechanism of the illustrative embodiments has several advantagesover the current state of the art. The mechanism is not dependent on anexternal network request and does not add to protocol load. If protocolrequests are being processed, that is known definitively. The servicewill never be characterized as unresponsive simply because the latencyof particular requests or types of requests has increased. The mechanismwill never restart a service under heavy load if reasonable forwardprogress is being made. The service can monitor state internally, whichwould be difficult or impossible to monitor externally. Examples includeif a particular client's requests are stalled or if a particularoperation is not progressing. This allows more precise and granularcorrective actions. For instance, a stalled client can be migrated toanother node rather than restarting the entire service. Problems with aparticular type of request can indicate implementation errors in theprotocol.

The illustrative embodiments may be utilized in many different types ofdata processing environments. In order to provide a context for thedescription of the specific elements and functionality of theillustrative embodiments, FIGS. 1 and 2 are provided hereafter asexample environments in which aspects of the illustrative embodimentsmay be implemented. It should be appreciated that FIGS. 1 and 2 are onlyexamples and are not intended to assert or imply any limitation withregard to the environments in which aspects or embodiments of thepresent invention may be implemented. Many modifications to the depictedenvironments may be made without departing from the spirit and scope ofthe present invention.

FIG. 1 depicts a pictorial representation of an example clustered filesystem in which aspects of the illustrative embodiments may beimplemented. Clustered file system 100 may include a network ofcomputers in which aspects of the illustrative embodiments may beimplemented. The clustered file system 100 contains at least one network102, which is the medium used to provide communication links betweenvarious devices and computers connected together within clustered filesystem 100. The network 102 may include connections, such as wire,wireless communication links, or fiber optic cables.

In the depicted example, server 104 and server 106 are connected tonetwork 102 along with storage units 108, 109. In addition, clients 110,112, and 114 are also connected to network 102. These clients 110, 112,and 114 may be, for example, personal computers, network computers, orthe like. In the depicted example, server 104 provides data, such asboot files, operating system images, and applications to the clients110, 112, and 114. Clients 110, 112, and 114 are clients to server 104in the depicted example. Clustered file system 100 may includeadditional servers, clients, and other devices not shown.

In one embodiment, storage units 108, 109 are network-attached storage(NAS) device, and servers 104, 106 allow clients 110, 112, 114 to accessthe NAS devices. Storage and access may be combined on one node. Theprotocol service is a software layer existing on the server and clientwhere the server provides the service and where the client accesses theservice. In the depicted example, servers 104, 106 provide the protocolservice to clients 110, 112, 114 to access NAS devices. In oneillustrative embodiment of the clustered file system 100, any of theservers 104, 106 can serve any of the clients 110, 112, 114 to provideaccess to any of the NAS devices 108, 109.

In the depicted example, clustered file system 100 is the Internet withnetwork 102 representing a worldwide collection of networks and gatewaysthat use the Transmission Control Protocol/Internet Protocol (TCP/IP)suite of protocols to communicate with one another. At the heart of theInternet is a backbone of high-speed data communication lines betweenmajor nodes or host computers, consisting of thousands of commercial,governmental, educational and other computer systems that route data andmessages. Of course, the distributed data processing system 100 may alsobe implemented to include a number of different types of networks, suchas for example, an intranet, a local area network (LAN), a wide areanetwork (WAN), or the like. As stated above, FIG. 1 is intended as anexample, not as an architectural limitation for different embodiments ofthe present invention, and therefore, the particular elements shown inFIG. 1 should not be considered limiting with regard to the environmentsin which the illustrative embodiments of the present invention may beimplemented.

FIG. 2 is a block diagram of an example data processing system in whichaspects of the illustrative embodiments may be implemented. Dataprocessing system 200 is an example of a computer, such as client 110 inFIG. 1, in which computer usable code or instructions implementing theprocesses for illustrative embodiments of the present invention may belocated.

In the depicted example, data processing system 200 employs a hubarchitecture including north bridge and memory controller hub (NB/MCH)202 and south bridge and input/output (I/O) controller hub (SB/ICH) 204.Processing unit 206, main memory 208, and graphics processor 210 areconnected to NB/MCH 202. Graphics processor 210 may be connected toNB/MCH 202 through an accelerated graphics port (AGP).

In the depicted example, local area network (LAN) adapter 212 connectsto SB/ICH 204. Audio adapter 216, keyboard and mouse adapter 220, modem222, read only memory (ROM) 224, hard disk drive (HDD) 226, CD-ROM drive230, universal serial bus (USB) ports and other communication ports 232,and PCI/PCIe devices 234 connect to SB/ICH 204 through bus 238 and bus240. PCI/PCIe devices may include, for example, Ethernet adapters,add-in cards, and PC cards for notebook computers. PCI uses a card buscontroller, while PCIe does not, ROM 224 may be, for example, a flashbasic input/output system (BIOS).

HDD 226 and CD-ROM drive 230 connect to SB/ICH 204 through bus 240. HDD226 and CD-ROM drive 230 may use, for example, an integrated driveelectronics (IDE) or serial advanced technology attachment (SATA)interface. Super I/O (SIO) device 236 may be connected to SB/ICH 204.

An operating system runs on processing unit 206. The operating systemcoordinates and provides control of various components within the dataprocessing system 200 in FIG. 2. As a client, the operating system maybe a commercially available operating system such as Microsoft Windows 7(Microsoft and Windows are trademarks of Microsoft Corporation in theUnited States, other countries, or both). An object-oriented programmingsystem, such as the Java programming system, may run in conjunction withthe operating system and provides calls to the operating system fromJava programs or applications executing on data processing system 200(Java is a trademark of Oracle and/or its affiliates.).

As a server, data processing system 200 may be, for example, an IBM®eServer™ System p® computer system, running the Advanced InteractiveExecutive (AIX®) operating system or the LINUX operating system (IBM,eServer, System p, and AIX are trademarks of International BusinessMachines Corporation in the United States, other countries, or both, andLINUX is a registered trademark of Linus Torvalds in the United States,other countries, or both). Data processing system 200 may be a symmetricmultiprocessor (SMP) system including a plurality of processors inprocessing unit 206. Alternatively, a single processor system may beemployed.

Instructions for the operating system, the object-oriented programmingsystem, and applications or programs are located on storage devices,such as HDD 226, and may be loaded into main memory 208 for execution byprocessing unit 206. The processes for illustrative embodiments of thepresent invention may be performed by processing unit 206 using computerusable program code, which may be located in a memory such as, forexample, main memory 208, ROM 224, or in one or more peripheral devices226 and 230, for example.

A bus system, such as bus 238 or bus 240 as shown in FIG. 2, may becomprised of one or more buses. Of course, the bus system may beimplemented using any type of communication fabric or architecture thatprovides for a transfer of data between different components or devicesattached to the fabric or architecture. A communication unit, such asmodem 222 or network adapter 212 of FIG. 2, may include one or moredevices used to transmit and receive data. A memory may be, for example,main memory 208, ROM 224, or a cache such as found NB/MCH 202 in FIG. 2.

Those of ordinary skill in the art will appreciate that the hardware inFIGS. 1 and 2 may vary depending on the implementation. Other internalhardware or peripheral devices, such as flash memory, equivalentnon-volatile memory, or optical disk drives and the like, may be used inaddition to or in place of the hardware depicted in FIGS. 1 and 2. Also,the processes of the illustrative embodiments may be applied to amultiprocessor data processing system, other than the SMP systemmentioned previously, without departing from the spirit and scope of thepresent invention.

Moreover, the data processing system 200 may take the form of any of anumber of different data processing systems including client computingdevices, server computing devices, a tablet computer, laptop computer,telephone or other communication device, a personal digital assistant(PDA), or the like. In some illustrative examples, data processingsystem 200 may be a portable computing device that is configured withflash memory to provide non-volatile memory for storing operating systemfiles and/or user-generated data, for example. Essentially, dataprocessing system 200 may be any known or later developed dataprocessing system without architectural limitation.

FIG. 3 is a block diagram illustrating a protocol service in accordancewith an illustrative embodiment. Protocol service 310 establishes a highpriority recovery thread 311. If the service is capable of anyprocessing, then high priority recovery thread 311 executes first.Protocol service 310 establishes health counters 312, which count totalprotocol requests in and total protocol requests out with respect to NASdevice 320. Protocol service 310 establishes health counters 312 foreach protocol operation type and for each client.

Recovery thread 311 monitors health counters 312 on a periodic basis andkeeps track of forward progress and rates. Recovery thread 311 then usesthis data to categorize the health of protocol service 310. In oneexample embodiment, recovery thread 311 may categorize the health of theservice as green, yellow, or red. For example, recovery thread 311 maycategorize the health of the service as green if the health counters 312indicate that forward progress is being made with protocol requests atan acceptable rate. Recovery thread 311 may categorize the health of theservice as red if the health counters 312 indicate that no total forwardprogress is being made. Recovery thread 311 may categorize the health ofthe service as yellow if the health counters 312 indicate that forwardprogress is being made but with heavy protocol load conditions or noprogress is being made on certain protocol operations.

High priority recovery thread 311 publicizes the category of the healthof the service as health condition 315. In one example embodiment,recovery thread 311 may publicize health condition 315 by writing thehealth condition 315 to cluster file system. In an alternativeembodiment, recovery thread 311 may multicast health condition 315 onthe network or process health condition 315 internally within protocolservice 310.

If the health condition 315 is green, then protocol service 310 and NASdevice 320 do not take corrective action. If the health condition 315 isred, then protocol service 310 restarts. In one example embodiment, thisonly occurs when no total forward progress is being made, i.e., theservice in total is thrashing. An outside source (not shown) mayinitiate the restart or protocol service 310 my initiate its ownrestart. If the health condition 315 is yellow, then protocol service310 may take a variety of actions, such as moving some or all of theclients.

As will be appreciated by one skilled in the art, the present inventionmay be embodied as a system, method, or computer program product.Accordingly, aspects of the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module,” or “system.” Furthermore,aspects of the present invention may take the form of a computer programproduct embodied in any one or more computer readable medium(s) havingcomputer usable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CDROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, in abaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Computer code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, radio frequency (RF), etc., or anysuitable combination thereof.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java™, Smalltalk™, C++, or the like, and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer, or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to the illustrativeembodiments of the invention. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions thatimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus, or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

FIG. 4 is a flowchart illustrating operation of a protocol service inaccordance with an illustrative embodiment. Operation begins (block400), and the protocol service establishes a high priority recoverythread (block 401). The high priority recovery thread initializes healthcounters (block 402).

The high priority recovery thread then monitors progress and rates(block 403) and updates the health counters (block 404). The highpriority recovery thread then determines whether a predetermined periodof time expires (block 405). If the period does not expire, operationreturns to block 403 to continue to monitor progress and rates.

If the period expires in block 405, the high priority recovery threadcategorizes the health of the service (block 406) and publicizes thehealth of the service (block 407). For example, the recovery thread maycategorize the health of the service as green if the health countersindicate that forward progress is being made with protocol requests atan acceptable rate. The recovery thread may categorize the health of theservice as red if the health counters indicate that no total forwardprogress is being made. The recovery thread may categorize the health ofthe service as yellow if the health counters indicate that forwardprogress is being made but with heavy protocol load conditions.

Thus, in the illustrative embodiment, the protocol service determinesthe color category of the health of the service (block 408). If thehealth of the service is categorized as green, operation returns toblock 402 to initialize the health counters and continue monitoring.

the health of the service is categorized as yellow in block 408, theprotocol service moves clients to another server (block 409), andoperation returns to block 402 to initialize the health counters andcontinue monitoring.

If the health of the service is categorized as red in block 408, theprotocol service restarts (block 410). Thereafter, operation ends (block411).

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

As noted above, it should be appreciated that the illustrativeembodiments may take the form of an entirely hardware embodiment, anentirely software embodiment or an embodiment containing both hardwareand software elements. In one example embodiment, the mechanisms of theillustrative embodiments are implemented in software or program code,which includes but is not limited to firmware, resident software,microcode, etc.

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards,displays, pointing devices, etc.) can be coupled to the system eitherdirectly or through intervening I/O controllers. Network adapters mayalso be coupled to the system to enable the data processing system tobecome coupled to other data processing systems or remote printers orstorage devices through intervening private or public networks. Modems,cable modems and Ethernet cards are just a few of the currentlyavailable types of network adapters.

The description of the present invention has been presented for purposesof illustration and description, and is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Theembodiment was chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method, in a data processing system, forprotocol servicing in network attached storage, the method comprising:establishing, by a protocol service executing in the data processingsystem in a clustered file system, a high priority recovery thread;monitoring, by the high priority recovery thread, health counters thatcount total requests in and total requests out for a client accessing anetwork-attached storage device via the protocol service; determining,by the high priority recovery thread, a category of health of theprotocol service based on the health counters; and taking correctiveaction based on the category of health of the protocol service.
 2. Themethod of claim 1, wherein taking corrective action comprises moving atleast one client to another protocol service responsive to the categoryof health of the protocol service being a first category.
 3. The methodof claim 1, wherein taking corrective action comprises restarting theprotocol service responsive to the category of health of the protocolservice being a second category.
 4. The method of claim 3, wherein thenetwork-attached storage device restarts the protocol service.
 5. Themethod of claim 1, further comprising taking no corrective actionresponsive to the category of health of the protocol service being athird category.
 6. The method of claim 1, further comprising:publicizing the category of health of the protocol service.
 7. Themethod of claim 6, wherein publicizing the category of health of theprotocol service comprises writing the category of health of theprotocol service to the cluster file system.
 8. The method of claim 6,wherein publicizing the category of health of the protocol servicecomprises multicasting the category of health of the protocol service.9. The method of claim 1, wherein monitoring health counters comprisesmonitoring health counters for each client accessing thenetwork-attached storage device via the protocol service.
 10. The methodof claim 1, wherein monitoring health counters comprises monitoringhealth counters for each protocol operation type.
 11. A computer programproduct comprising a computer readable storage medium having a computerreadable program stored therein, wherein the computer readable program,when executed on a computing device, causes the computing device to:establish, by a protocol service executing in the data processing systemin a clustered file system, a high priority recovery thread; monitor, bythe high priority recovery thread, health counters that count totalrequests in and total requests out for a client accessing anetwork-attached storage device via the protocol service; determine, bythe high priority recovery thread, a category of health of the protocolservice based on the health counters; and take corrective action basedon the category of health of the protocol service.
 12. The computerprogram product of claim 11, wherein taking corrective action comprisesmoving at least one client to another protocol service responsive to thecategory of health of the protocol service being a first category. 13.The computer program product of claim 11, wherein taking correctiveaction comprises restarting the protocol service responsive to thecategory of health of the protocol service being a second category. 14.The computer program product of claim 13, wherein the network-attachedstorage device restarts the protocol service.
 15. The computer programproduct of claim 11, wherein the computer readable program furthercauses the computing device to: take no corrective action responsive tothe category of health of the protocol service being a third category.16. The computer program product of claim 11, wherein the computerreadable program further causes the computing device to: publicizing thecategory of health of the protocol service.
 17. The computer programproduct of claim 16, wherein publicizing the category of health of theprotocol service comprises writing the category of health of theprotocol service to the cluster file system.
 18. The computer programproduct of claim 16, wherein publicizing the category of health of theprotocol service comprises multicasting the category of health of theprotocol service.
 19. The computer program product of claim 11, whereinmonitoring health counters comprises monitoring health counters for eachclient accessing the network-attached storage device via the protocolservice.
 20. An apparatus, comprising: a processor; and a memory coupledto the processor, wherein the memory comprises instructions which, whenexecuted by the processor, cause the processor to: establish, by aprotocol service executing in the data processing system in a clusteredfile system, a high priority recovery thread; monitor, by the highpriority recovery thread, health counters that count total requests inand total requests out for a client accessing a network-attached storagedevice via the protocol service; determine, by the high priorityrecovery thread, a category of health of the protocol service based onthe health counters; and take corrective action based on the category ofhealth of the protocol service.